A vehicle speed control system for controlling a vehicle on a chassis dynamometer is comprised of a controller which is arranged to receive a vehicle speed command, to obtain an anticipated vehicle speed command from the vehicle speed command taking account of a delay factor of a control system of the vehicle, to calculate a driving force a driving force command from the anticipated vehicle speed command, to obtain an accelerator opening command from a previously stored driving force characteristic map based on the driving force command and a detected vehicle speed, and to control an accelerator opening of the vehicle according to the accelerator opening command so as to adjust the detected vehicle at the vehicle speed command.